The mucosal surface of the bronchi, gastrointestinal tract, urogenital system, or the like has a strong mucosal immune system in which secretory IgA play a major role in protecting the organism against microorganisms such as bacteria and viruses, and many foreign antigens including dietary proteins and the like. The secretory IgA, unlike IgA in serum, exists in the form of a J-chain-containing dimeric IgA (2IgA-J) bound with a secretory component (SC; or secretory piece) (2IgA-J-SC) and is contained in large amounts in saliva, tears, nasal secretion, breast milk, and secretions from the bronchi, intestines, or the like. Lymphoid tissues in such mucosal surface are called mucosa-associated lymphoid tissues and play a central role in the induction of IgA production. In mucosal immunity, B cells activated by antigenic stimulation in Peyer's patch, a representative intestinal mucosa-associated lymphoid tissue, or the like are redistributed in the mucosal surfaces of not only the intestines but also the exocrine glands, bronchi, and urogenital system through systemic circulation and then differentiated into plasma cells, IgA-producing cells to produce dimeric IgA. The produced dimeric IgA is further converted into secretory IgA through binding with a secretory component produced in mucosal epithelial cells, and secreted from within the mucosa to lumens or the outside of the organism. The secretory component has been known to be essential for secreting dimeric IgA to lumens or the outside of the organism.
Thus, a food component or composition that induces and establishes dimeric IgA production and secretory component production in the mucosa of the bronchi, gastrointestinal tracts, urogenital system, or the like can be expected to increase the amount of secretory IgA production or secretory IgA secretion from the mucosa to lumens or the outside of the organism and thereby enhance the biophylaxis capacity. The enhancement of such a biophylaxis capacity of mucosal immunity is particularly useful for the prevention of pathogen invasion into bodies, the prevention of occurrence of food allergy, and so on.
The present inventors have found, for example, fructo-oligosaccharide and a composition thereof as substances promoting secretory IgA production (Patent Document 1). This fructo-oligosaccharide is one of the few food components that have been reported about their influence on secretory component production. On the other hand, bifidobacteria Bifidobacterium longum and Bifidobacterium breve have heretofore been known to stimulate IgA production in Peyer's patch cells (Patent Document 2). Moreover, the present inventors have previously found that Bifidobacterium longum OLB 6001 strain separated from human adult feces has an IgA production-stimulating ability (Non-Patent Document 1). This bifidobacterium Bifidobacterium longum OLB 6001 strain is identical to Bifidobacterium longum No. 7 (accession No. FERM P-13610) reported by the group of the present inventors (Patent Document 3). However, the further emergence of a composition for immunostimulation having higher immunostimulating effect, which exceeds even those of these bifidobacteria, is still demanded.    Patent Document 1: JP Patent Publication (Kokai) No. 2003-201239A (2003)    Patent Document 2: JP Patent Publication (Kokoku) No. 7-106142B (1995)    Patent Document 3: JP Patent Publication (Kokai) No. 7-69907A (1995)    Non-Patent Document 1: Takahashi T., Nakagawa E., Nara T., Yajima T. and Kuwata T., Biosci. Biotechnol. Biochem., 62 (1), (1998) p. 10-15